The goal of the proposed research is to study the regulation of expression of cell surface proteins in cultured mouse cell lines. The approach will be to analyze a number of mutants that have undergone alterations in the expression of either the H-2 proteins or Beta2-microglobulin (Beta2Mu). Most of the mutants were specifically isolated for the expression of predetermined phenotypes in my lab; some others arose spontaneously, and were identified fortuitously. The following kinds of mutants will be analyzed in greater detail using biochemical, immunological, somatic cell genetic, and molecular biological techniques: (1) Hemizygous mutants (mutants that arise from a heterozygous cell line, but fail to express either parental set of H-2 genes) will be analyzed to confirm our hypothesis that at least some of them arise by mitotic recombination resulting in homozygosity for the expressed H-2 antigen genes. (2) Mutants that exhibit disorders in the expression of H-2 antigens and Beta2Mu. Our analysis of these mutants has resulted in the realization that unlike most H-2 antigens, H-2Ld and H-2Db appear on the cell surface without detectable Beta2Mu. The molecular defect in the mutants will be analyzed in greater detail. The unique properties of H-2Ld and H-2Db that allow them to be expressed on the cell surface without Beta2Mu will also be determined. (3) Mutants that do not express Beta2Mub. These mutants appear to fall into three general classes. The molecular basis of these mutations will be analyzed in greater detail. We believe that the cell surface antigens of somatic cells offer some very favorable properties for genetic analysis and it is our hope that through an analysis of these mutations, we can gain a deeper understanding of the mechanisms of regulation of gene expression in animal cells.